Code-Splitting of shortcuts.js for main.js reduction

What does this MR do?

It code-splits the loading of the general shortcuts.js part so it is only loaded on the pages where its actually needed. Currently we already have the condition when it is needed and this simply instead of instantiating it loads first the bundle. Right now the saving is just 1kb but this is needed to have then at some point the bigger improvement along the other behavior parts. See &3423 for more information.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #246540 (closed)